Serpinc1 or antithrombin III (AT3) is a member of the serine proteinase inhibitor (serpin) superfamily Serpinc1 is a plasma protease inhibitor that inhibits thrombin as well as other activated serine proteases of the coagulation system, such as factors X, IX, XI, XII and VII and, thus, regulates the blood coagulation cascade (see, e.g., FIG. 1). The anticoagulant activity of Serpinc1 is enhanced by the presence of heparin and other related glycosaminoglycans which catalyze the formation of thrombin:antithrombin (TAT) complexes.
Bleeding disorders, either inherited or acquired, are conditions in which there is inadequate blood clotting. For example, hemophilia is a group of hereditary genetic bleeding disorders that impair the body's ability to control blood clotting or coagulation. Hemophilia A is a recessive X-linked genetic disorder involving a lack of functional clotting Factor VIII and represents 80% of hemophilia cases. Hemophilia B is a recessive X-linked genetic disorder involving a lack of functional clotting Factor IX. It comprises approximately 20% of haemophilia cases. Hemophilia C is an autosomal genetic disorder involving a lack of functional clotting Factor XI. Hemophilia C is not completely recessive, as heterozygous individuals also show increased bleeding.
Although, at present there is no cure for hemophilia, it can be controlled with regular infusions of the deficient clotting factor, e.g., factor VIII in hemophilia A. However, some hemophiliacs develop antibodies (inhibitors) against the replacement factors given to them and, thus, become refractory to replacement coagulation factor. Accordingly, bleeds in such subjects cannot be properly controlled.
The development of high-titer inhibitors to, for example, factor VIII and other coagulation factors, is the most serious complication of hemophilia therapy and makes treatment of bleeds very challenging. Currently, the only strategies to stop bleeds in such subjects are the use of “bypassing agents” such as factor eight inhibitor bypass activity (FEIBA) and activated recombinant factor VII (rFVIIa), plasmapheresis, continuous factor replacement, and immune tolerance therapy, none of which are completely effective. Accordingly, there is a need in the art for alternative treatments for subjects having a bleeding disorder, such as hemophilia.